Reliability and residual service life of the steampipe welded joints at the temperature of 540°C

In this paper the influence is described of the 1/2Cr-1/2Mo-1/4V steel pipe joints, welded with electrodes of the same composition (with long-term exposure to the temperature of 540°C and the pressure of 14MPa), on life decreases of steampipe with 273 mm in diameter and 32 mm wall thickness. To the prediction of welded joint lifetimes the model of separated diffusion and fatigue failure was applied. The results show that the prolongation of intervals between the putting out of operation tends to welded joints lifetime elongation. It is also indicated that in lower weld structural stability values for fatigue processes are predominant being caused by a weld failure, and in higher structural stability values the failure is caused by creep processed.